Air compressors



May 29, 1956 G. SZEKELY AIR COMPRESSORS 2 Sheets-Sheet 1 Filed Nov. 12, 1952 A itorney May 29, 1956 G. SZEKELY AIR COMPRESSORS 2 Sheets-Sheet 2 Filed Nov. 12, 1952 I nventor oljg SicKc A tto ney AER CQMPRESSORS George Szekely, Tel Aviv, Israel Application November 12, 1952, Serial No. 319,947

Claims priority, application Austria November 22, 195i 6 Claims. (Cl. fill-55) The present invention is a further development of the electrically driven compressor as described in my prior British Patent No. 428,632 and U. S. A. Patent No. 2,117,863, according to which the suction stroke of a membrane is effected by the vibrating armature of an alternating current electromagnet while the compressing stroke is effected by a metallic spring or a resilient rubber block compressed during the suction stroke. In the said U. S. A. patent I have proposed to bring the performance of the spring in harmony with the vibrating armature. in so doing I considered the fact that towards the end or" the compression stroke the load increases and is thus likely to destroy the resonance between the armature and the spring, if the spring has a linear compression characteristic. Such destruction of the resonance, however, is prevented if the pressure of the spring likewise increases or has a non-linear characteristic. It is an object of the present invention to improve the construction and operation of the spring having a non-linear characteristic.

in order to make the invention better understood, I wish to more clearly expound the requirements involved.

It has been repeatedly attempted to effect the alternating movement necessary for driving the plunger or the membrane of compressors by the armature of an electromagnet. The arrangement of electric switches for this purpose proved to be unsuccessful and for the purpose of this invention only the movement is to be considered which originates from the armature of an electromagnet energised by an alternating current. In this case of course the number of oscillations and their velocity is quite high, so that they are normally not suitable for doing useful compression work.

The most advantageous arrangement is to let the attracted armature effect the suction stroke, while the compression stroke is effected during the return of the armature from the poles. While the armature is attracted the surplus of the force of attraction is stored in a spring, the tension of which is then utilised for the compression stroke. The attraction of the armature and its return movement proceed in accordance with the number of oscillations of the alternating current, so that e. g. with 50 periods, 100 suction strokes and 100 compression strokes are produced. The output of such compressors depends in principle: on the dimensions of the magnet, the amplitude of the oscillations, the quality of the oscillating spring, and the construction of the compressing means (membrane). A close examination of these conditions has shown, that the dimensions of the magnet are limited for practical purposes, since the magnetic system swinging in the alternating field creates a considerable dislocation of the phase which lowers quite considerably the factor cos g of the output. With small electric machines this loss is negligible. But oscillating compressors yielding an output of about 6 gauge atmospheres and about 100 liters per minute of sucked in air, must be excessively dimensioned and be equipped with additional means for correcting the considerable destructive current.

The size of the magnet depends mainly on the amperage Z,'?47,789 Patented May 2%, 1956 of the current flowing through its windings, and the amperage depends on the distance between the poles of the magnet and the armature, this distance representing the actual working stroke. From the viewpoint of the compression output it would, therefore, be advantageous to keep the air gap between the magnet and the armature as great as possible. However, this would considerably impair the construction and operation and would cause noise. An oscillation of the armature with an amplitude of e. g. 2-3 mm. would assume an enormous velocity and lessen the life of all movable parts.

The position of the path of the oscillation of the armature, the ends of which path are not determined by any mechanical means, depends on the varying pressure on the medium to be compressed. With the increase or decrease of the counterpressure the middle of the oscillation shifts without any change of the amplitude of the oscillation. This shifting affects the magnetic driving conditions in a way that with an increase or decrease of the counterpressure, a decrease or increase of the consumed electrical energy is obtained. Thus the compression Work regulates itself by the electromagnetic driving system without employing the common controlling means, as maximal valves, pressure switches, or the like.

Experience has shown that only relatively small oscillations of the armature in the alternating field offer a useful drive. To utilise the resulting small driving strokes, the power has to be stored in a spring having a non-linear characteristics. Since generally the curvature of the compression line of the working medium prevents the creation of harmonic oscillations, the distorting influence of the compression had to be compensated by the resilient arrangement of the system in such a manner as to impart to the spring a non-linear characteristic suitable for this purpose.

With resilient bodies the characteristic of which deviates upwardiy, it is generally possible to bring the pseudoharmonic oscillation, generally present with these cornpressors, nearer to the harmonic ones than is possible when using springs having a linear characteristic. With varying pressures, characteristic lines are obtained, the rise of which within the working limits changes less than is the case if springs of a linear characteristics are used. Thus if resilient bodies having a non linear characteristic, are used, the variations of the compression will less affect the frequency of the oscillating system than linear springs. The magnitude of the amplitude of the oscillations re mains also approximately constant, so that variations of compression cause only a small lowering of the output.

The suitability of such springs has been founded on theoretical considerations. But in practice it has been difficult to determine springs for minimal strokes having a suitable non-linear characteristic.

From what it has been said above it follows that for a satisfactory construction of oscillating compressors it is required that a spring be used which is adapted to store and release the magnetic pull with the least delay, whereby the non-linear characteristic of the work of this spring is adjusted to the magnetic conditions as well as to the counterpressure of the compressed medium. Hereby the minimal vibratory movements (oscillations) of the armature are transmitted by a rigid system to a membrane compressor and thus transformed into useful compression-work.

According to the invention an appropriate spring from rubber or another elastic material is made in the shape of a ringlike body. The border of this ring is fixed between the two faces of two rigid plates movable relative to each other, and one face of the rings is conical towards the middle thereof. The generatrix of the conical face may be straight or curved. To this ringlike spring which is fixed between the two rigid plates is given an aymarse appropriately defined precompression whereby the system is brought into a zero position from which the effective working stroke (the amplitude of oscillation) starts. The height of the conical face corresponds in each case to the range of the precompression. The ringlike spring may originally have rough dimensions and be then adjusted in a simple manner by an exact adjustment of the plates and thus changing the angle of the conical face of the ring, whereby the spring comes into the proper working range. The diameter of the spring should be approximately coextensive with the length of the armature. This assures the armature against tilting vibrations and keeps it in a parallel position to the poles of the magnet.

This arrangement of the spring proves to be effective already with amplitudes above 0.1 mm. The small lifting strokes of 0.l1 mm. are most effectively transmitted onto a membrane by a central rod passed through the opening of the ringlike spring and attached with its lower end to the center of the armature and with the upper end to the membrane.

The membrane is of a soft and bendable material, e. g. rubber, plastic or the like, and has a thickened middle portion enclosing an embedded plate-like end of the rod. The membrane is thus stiff like a plunger, the thin border of which is fixed leaving a narrow membrane ring between the thickened portion and fixing means.

The precompressed spring urges the even upper face of the stiffened membrane against a counterplate carry ing the suction and pressure-valves. The plunger-membrane closely pressed against the counterplate prevents the creation of dead spaces which of course should at any rate be obviated with small working strokes. Detrimental deformations of the stiffened membrane do not occur even after long use, so that lastingly unchanged working conditions are safeguarded. The described membrane forming the compression member affords the advantages of a plunger without any lubrication being needed. The simple membrane having e. g. an effective diameter of 80 mm. and a stroke of 0.5 mm. supplies a volume of about 2.5 cubic centimeters with an alternating current of 50 periods (100 vibrations in the second) gives a suction output of about 15 liters in the minute. The compression output depends on the force of the magnet, which for instance attracts its armature at a distance 0.5 mm. with a force of about 100 kg, in which case the above membrane reaches an output of 2 gauge atmospheres pressure.

It is self-understood that dead spaces are to be avoided in the valves as well. For this reason the valves are arranged according to the construction described in close proximity of the membrane. The valves themselves consist of small plates which open and close with the fre' quency of the pulsating air-stream.

In Fig. l the new air compressor is shown in a vertical section.

Fig. 2 is a cross section on the line AB of Fig. 1.

Fig. 3 demonstrates graphically the comparative outputs of a linear, a non-linear, and a spring according to the invention.

For a better understanding of the invention, Fig. 3 is first referred to in which the ordinates give the output of the compressor in cubic centimeters per hour, and the abscissae the pressure in atmospheres. In this figure the dash line I shows the output of a linear spring, and line [I that of a non-linear spring. It is apparent that according to line II the spring works appreciably more favourably than according to line I, since in case II with increasing pressure the raised quantity does not so quickly diminish. In contradistinction line III illustrates the path of the output of the now described membranecompressor. The characteristic line is partly straight and horizontal, and this just along the useful range of pressure (from 0.4-1.2), within which range the supplied quantity of air remains constant. This means that for example in the spraying of liquids by means of compressed air, a constant quantity of liquid is supplied ir respective of the varying air pressure.

The details of the construction of the compressor are seen from Fig. 1. On the quadrangular base plate 1 is fastened the double U-shaped electromagnet 2, through which flows an alternating current. Near the corners of the base plate there are provided holes through which are passed four vertical bolts 3. These bolts carry at a certain distance from the upper end of the magnet 2 a horizontal plate 1% which has a central opening. On this plate is seated a ring-like body 9 from rubber covered by a metallic plate 8 of equal size which is likewise centrally pierced. Above the magnet 2 and below the plate 10 there is arranged an armature 4-. In the middle of the armature 4 is screwed the lower end of a pin 5, the upper end of which is enlarged to a rigid round plate 6. Plate 6 is embedded in a likewise round thickened central part 7 of a rubber-membrane 7. Prior to screwing the pin 5 into the armature 4, the round metallic plate 8, the resilient rubber ring 9, the quadrangular metallic plate 10, and the screw nuts 11, 11' and 12 are slid thereon. The rubber membrane 7 now rests with its thickened central portion on the plate 8, the pin 5 passing freely through the different central openings, whereby the armature is freely held in the position described above. The nuts 11, ll serve to keep the plate 8 snugly against the membrane 7, 7' and nut 12 serves for fixing the armature 4 to its pin 5. The four bolts 3 are passed through the quadrangular plate 10 which is clamped to them by the nuts 3, 3". By adjusting these nuts, the plate 10 and therefore also the rubber ring 9 and its second covering plate 8 can be more or less urged against the membrane 7. The upper surface of the rubber ring is sloping downwardly and inwardly, so that the metallic plate 8 rests at first on the outer margin of the rubber ring 9. By pressing the rubber ring against this plate (by means of the nuts 3', 3 on the bolts 3), the surface on which this plate rests, grows larger towards the middle whereby the rubber-ring is compressed and pretensioned to a desired degree, which thanks to the mentioned slope can be precisely determined. Armature, pin, upper clamping plate and membrane move as a unit like a rigid plunger, apart from the narrow margin of the membrane between a plate 13 and the thickened portion 7' of the membrane. The plate 13 has a central circular opening through which the part 7 projects downward.

The border of the rubber membrane 7 is clamped between the iron plate 13 fastened to the bolts 3 and an upper metallic plate 14 which is likewise fastened to the bolts 3. Plate 14 carries the suction valve 15 and the pressure valve 16. These two valves consist of thin light small plates. On plate 14 is fastened by screws 20 a narrow plate 19 carrying the admission and outlet ducts 17, 18. The four screw bolts 3 thus connect the parts 1, 10, 13, 14 together. The outer diameter of the rubber ring 9 is advantageously at least as long as the armature 4. Thereby any inclination of the armature will not so adversely affect the membrane 7 as would be the case with a shorter diameter of the rubber ring. The magnitude of the gap between the armature 4 and the magnet 2 may, if needed, be adjusted by means of the screw-nuts on the base plate and raising or lowering of the magnet fastened thereon.

The new electrical compressor is significant by its output and durability; the returning force is accumulated or taken up in aresilient body in a degree proportionate to the magnetic and compression conditions and the smallest raising movements are transmitted to the centrally stiffened membrane.

What I claim is:

1. In an air compressor the combination of: electromagnetic means including an energizable electromagnet and a vibratile armature operatively associated with said electromagnet, a membrane rigidly connected with said armature, said membrane and said armature being normally in a first position, and resilient means interposed between said armature and 5 id membrane, said resilient means being compressed upon energization of said electromagnet and the resulting attraction of said armature to said electromagnet into a second position, said resilient means returning said membrane and said armature to said first position upon deenergization of said electromagnet, said resilient means including an annular resilient member, at least one end face of said annular resilient member conically tapering towards its center.

2. In an air compressor as claimed in claim 1, said resilient member being stationarily mounted between said membrane and said armature.

3. In an air compressor as claimed in claim 1, said resilient means including adjustable precompression means for adjustably precompressing said resilient memher.

4. In an air compressor as claimed in claim 1, said membrane comprising a central, substantially rigid portion, a marginal portion and an annular portion intermediate said central and marginal portions, said central portion being rigidly connected to said armature, and means for stationarily fixing and clamping said marginal portion.

5. In an air compressor as claimed in claim 1, said annular, resilient member being of rubber and having an outer diameter substantially equal to the width of said electromagnet.

6. In an air compressor the combination of: a base plate, an energizable electromagnet mounted on said base plate, a plurality of bolts projecting from said base plate, a first plate having a central bore, means for adjustably fixing said first plate to said bolts, an annular rubber block mounted on said first plate, said annular rubber block having at least one end face conically tapering towards its center, a second plate having a central bore and resting on said rubber block, means for precompressing said rubber block between said first and second plates, a membrane mounted on said second plate, said membrane having a thickened, substantially rigid, central portion, a marginal portion and an annular portion intermediate said thickened and marginal portions, an armature opcratively associated with said electromagnet, a pin passing through said central bores of said first and second plates and rigidly connecting said armature to said thickened portion of said membrane, and means for fixedly clamping said marginal portions of said membrane, said membrane and said armature being normally in a first position, said rubber block being compressed between said first and second plates upon energization of said electromagnet and the resulting attraction of said armature to said electromagnet into a second position, said rubber block returning said membrane and said armature to said first position upon deenergization of said electromagnet.

References Cited in the file of this patent UNITED STATES PATENTS 1,847,085 Flint Mar. 1, 1932 1,978,866 Konig Oct. 30, 1934 2,117,863 Szekely May 17, 1938 2,229,038 Booth Ian. 21, 1941 FOREIGN PATENTS 428,632 Great Britain May 16, 1935 

